Biofuel blending reduces particle emissions from aircraft engines at cruise conditions

Compared to using conventional jet fuel, the use of a biofuel blend reduces aircraft engine particle emissions at cruising altitude by about 50–70 per cent. Aviation affects the climate as a result of aerosol and carbon dioxide emissions from fossil fuels. Biofuels could be a future source of aviation energy that is not dependent on fossilized carbon, but the environmental impact of these fuels, when used by planes in flight, has not yet been investigated. This study presents observational data gathered from directly behind an aircraft flying at cruise altitude and finds that, compared to using purely conventional fuel, a blend of conventional fuel and biofuel reduces aerosol particle emissions by 50 to 70 per cent. The authors also provide several aerosol parameters that will help transportation and climate modellers to assess whether the use of biofuels in aviation is a feasible strategy to mitigate climate change. Aviation-related aerosol emissions contribute to the formation of contrail cirrus clouds that can alter upper tropospheric radiation and water budgets, and therefore climate1. The magnitude of air-traffic-related aerosol–cloud interactions and the ways in which these interactions might change in the future remain uncertain1. Modelling studies of the present and future effects of aviation on climate require detailed information about the number of aerosol particles emitted per kilogram of fuel burned and the microphysical properties of those aerosols that are relevant for cloud formation2. However, previous observational data at cruise altitudes are sparse for engines burning conventional fuels2,3, and no data have previously been reported for biofuel use in-flight. Here we report observations from research aircraft that sampled the exhaust of engines onboard a NASA DC‐8 aircraft as they burned conventional Jet A fuel and a 50:50 (by volume) blend of Jet A fuel and a biofuel derived from Camelina oil. We show that, compared to using conventional fuels, biofuel blending reduces particle number and mass emissions immediately behind the aircraft by 50 to 70 per cent. Our observations quantify the impact of biofuel blending on aerosol emissions at cruise conditions and provide key microphysical parameters, which will be useful to assess the potential of biofuel use in aviation as a viable strategy to mitigate climate change.